The present invention relates generally to circuit interconnection methods, and more particularly, to orthogonal grid circuit interconnection methods using a two-layer interconnect pattern.
Prior an relating to the present invention involves what is known as multichip module-dielectric (MCM-D) technology, or high density multichip interconnect (HDMI) technology. In accordance with this technology, circuit layers are formed by photoetching sputtered aluminum or copper films applied to spun-on films of dielectric on a ceramic, metal or silicon substrate. Because the HDMI process requires many vacuum operations and etching sequences, completed circuits are very expensive.
A technique for applying all circuitry including power and ground on two layers was conceived by Dr. Leonard Schaper at the University of Arkansas. As described by Dr. Schaper, the technique uses HDMI processes to form the circuits, which includes etching of sputtered metal layers applied to dielectric films spun onto a rigid substrate. This technique, though producing circuits that are less expensive than conventional HDMI circuits because the number of layers is reduced to only two, is still costly because of the number of expensive vacuum sputtering and chemical etching steps that are required. The present invention combines several other known, less expensive processes not used in the Schaper technique, and employs only two layers to produce circuits having a very large format at very low cost.
Another example of the prior art includes what is known as multichip circuit-laminate (MCM-L), which constitutes fineline versions of more conventional printed wiring board (PWB) technology. Using this MCM-L technology, finer line features and smaller through-hole drills are used to produce relatively high density circuits. This technology is useful for moderate density circuits, but it cannot achieve the high density circuit capability of either HDMI or our invention.
Therefore it is an objective of the present invention to provide for improved circuit interconnection methods that combine relatively inexpensive processes and employ only two layers to produce circuits having a very large format at very low cost.